Owing to the spread of an FF (Front engine, Front wheel drive) car aimed at the development of a small lightweight car and also to an increase of a residential space in the car, an engine room of the car is increasingly forced to become small. Therefore electric auxiliary machines for use in the car are made increasingly small and lightweight. Further there is a growing demand for the development of high-performance and high-output electric auxiliary machines.
As representative electric auxiliary machines for use in the car, there are a fan-coupling apparatus which makes an optimum ventilation corresponding to the temperature of the engine and an alternator which receives the rotation of the engine with its belt and generates electricity, thus supplying an electric power to an electric load of the car and has a function of charging a battery. These electric auxiliary machines are used to efficiently utilize the rotational torque of an engine through a one-way clutch which is connected to an engine output shaft only when the engine is in a predetermined output state. The rotation-transmitting apparatus with a built-in one-way clutch mounted on the electric auxiliary machine for the car is frequently connected to and disconnected from the engine output shaft. When the rotation-transmitting apparatus with the built-in one-way clutch is connected to the engine output shaft, it has a high rotational speed. Consequently a high load is applied to the rotation-transmitting apparatus with the built-in one-way clutch, and it generates a large amount of heat and vibration. The use condition for the rotation-transmitting apparatus with the built-in one-way clutch has become strict as the car has come to have high performance and output.
Because the use condition for the rotation-transmitting apparatus with the built-in one-way clutch has become strict, when rolling bearings rotate, namely, when a roller clutch overruns, the hydrogen brittleness-caused peeling phenomenon is liable to occur with the rolling contact surfaces of balls and the rolling surfaces of inner and outer rings constructing the rolling bearing turning into white in the textures thereof. In addition, when the rolling bearings do not rotate, namely, when the roller clutch is locked, fretting wear is liable to occur at the contact portions between the rolling contact surfaces of the balls and the rolling surface of each of the inner and outer rings. Therefore grease which is enclosed in a space where the balls are mounted is desired to prevent the generation of the peeling and fretting wear.
The electric auxiliary machine on which the rotation-transmitting apparatus with the built-in one-way clutch is mounted is frequently installed on a lower portion of an engine room. Thus while a car is travelling, rainwater is liable to penetrate into the rotation-transmitting apparatus with the built-in one-way clutch. When the rainwater penetrates into the space in which the balls of rolling bearings are mounted, the rolling contact surfaces of the balls and the rolling surface of each of the inner and outer rings are liable to be corroded. Therefore the grease which is enclosed in the space in which the balls of the rolling bearings are mounted is required to have rust-preventing performance superior to that of grease which is used in other portions.
In the one-way clutch of the rotation-transmitting apparatus with the built-in one-way clutch for use in the alternator, the one using grease containing ether oil as its base oil (see patent document 1), the one using grease whose viscosity pressure coefficient is not less than a predetermined value (see patent document 2), and the one using grease containing synthetic oil whose kinematic viscosity at 40° C. is not more than 60 mm2/second as its base oil (see patent document 3) are known.
But in patent document 1, the one-way clutch using the grease containing the ether oil as its base oil has a problem that it has an insufficient low frictional wear property when the one-way clutch is in an overrun state. In the patent document 2, the use of the grease whose viscosity pressure coefficient is not less than the predetermined value is effective for securely realizing a locked state, but has a problem that the grease is incapable of sufficiently restraining wear in the overrun state. In the patent document 3, the grease containing the synthetic oil whose kinematic viscosity is low has an insufficient heat resistance. Thus it is difficult to use the grease for a long time.
Patent document 1: Japanese Patent Application Laid-Open No. 11-82688
Patent document 2: Japanese Patent Application Laid-Open No. 2000-234638
Patent document 3: Japanese Patent Application Laid-Open No. 2000-253620